Shaped like a peekytoe crab, it’s a half-millimeter across and it can crawl, jump, bend, and twist through tiny apertures. The edge of a coin provides an ample landscape for its crabby walk.
As the smallest remote-controlled walking robot ever created, this prototype micro robot brings the field of robotics one step closer to performing practical tasks within tight spaces, such as repairing small machines.
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“Our technology enables a variety of controlled motion modalities and can walk with an average speed of half its body length per second,” says the project’s lead theoretical researcher, Yonggang Huang, in a news release. “This is very challenging to achieve at such small scales for terrestrial robots.”
The research by engineers at Northwestern University in Evanston, Illinois was published on May 25 in the journal Science Robotics.
The micro robot’s elastic body is responsible for locomotion. Unlike many other robots, this crab wears no complex hardware or electrical components to power its locomotion. It’s made of a rubbery alloy with shape-retention properties. A thin glass coating squeezes the alloy into a slightly deformed shape. When researchers point a scanned laser beam at different locations on the crab’s body, those parts heat up and transform into their pre-deformed shape, according to the team’s news release. As the hot parts cool, the alloy bounces back to its deformed shape.
During this process, the alloy changes form rapidly, causing the tiny crab to move from one spot to another. In essence, the laser becomes a remote-control device that activates the crab and even sets it walking in a particular direction. Because they use a scanning laser—a laser beam that can be directed to make a particular path across a surface (similar to those used to create a 3D map of an uneven terrain)—the researchers can orchestrate the laser current’s direction. If the laser scans from left to right, for example, then the crab moves from right to left. And because this crab is so small, the heating and cooling action is more rapid than for a larger robot, enabling it to run faster, John A. Rogers, the project’s experimental lead, says in the news release.
A child’s pop-up book was the inspiration for the peekytoe crab’s assembly; Rogers and Huang developed the technique eight years ago. They started with prefabricated flat structures that they bonded onto a slightly stretched rubber substrate. When it relaxes, the stretched substrate buckles in a controlled manner, resulting in a pop-up action. In this case, the prefab crab-shaped structures caused the substrate to pop up into a corresponding three-dimensional crab shape.
The team chose a peekytoe crab shape simply for the fun of watching a minuscule robot wriggle in a crab-like fashion, but their three-dimensional printing technique could be used to mimic any animal or shape, the researchers say. They also developed millimeter-sized robots resembling inchworms, crickets, and beetles during this research.
The team is excited to see how the field of robotics will develop if such small microbots can be further developed to perform more complex tasks.
“You might imagine micro robots as agents to repair or assemble small structures or machines in industry or as surgical assistants to clear clogged arteries, to stop internal bleeding or to eliminate cancerous tumors—all in minimally invasive procedures,” Rogers says in the news release. Notably, his team also created the smallest human-made flying structure in 2021 with a winged microchip.